This invention relates generally to microwave devices and more particularly to analog phase shifters.
Phased array antennas include a large number of elements that emit phased signals to form a radio beam. The radio signal can be electronically steered by the active manipulation of the relative phasing of the individual antenna elements. This electrically steered beam concept applies to both the transmitter and the receiver. Phased array antennas are advantageous in comparison to their mechanical counterparts with respect to their speed, accuracy, and reliability. The replacement of gimbal-scanned antennas by their electronically scanned counterpart increases antenna survivability through more rapid and accurate target identification. Complex tracking exercises can also be accomplished rapidly and accurately with a phased array antenna system.
A phase shifter is an essential element, which controls the phase of a microwave signal, in a phased array antenna. A good performance and low cost phase shifter can significantly improve performance and reduce the cost of the phased array, which should help to transform this advanced technology from recent military dominated applications to commercial applications.
Previous patents that disclose ferroelectric phase shifters include U.S. Pat. Nos.: 5,307,033, 5,032,805, and 5,561,407. The phase shifters disclosed therein include one or more microstrip lines on a ferroelectric (voltage-tuned dielectric) substrate to produce the phase modulating. Tuning of the permittivity of the substrate results in phase shifting when a radio frequency (RF) signal passes through the microstrip line. Microstrip ferroelectric phase shifters suffer from high conducting losses, high modes, DC bias, and impedance matching problems. Coplanar waveguide (CPW) phase shifters made from voltage-tuned dielectric films, whose permittivity may be varied by varying the strength of an electric field on the substrate have also been disclosed.
B. T. Henoch and P. Tamm disclosed a 360xc2x0 varactor diode phase shifter in xe2x80x9cA 360xc2x0 Varactor Reflection Type Diode Phase Modulator,xe2x80x9dIEEE Trans. On Microwave Theory and Tech., Vol. MTT-19, January 1971, pp. 103-105. Their design included two parallel coupled series resonant circuits that were connected to a circulator by means of a quarter-wave transformer. The transformer equalizes the insertion loss. However, the phase shifter showed large frequency dependence at phase shifts between 0xc2x0 to 360xc2x0.
Ulriksson has modified the above design to optimize frequency response for all phase shifts up to 180xc2x0 by introducing a slight change in one of the parallel coupled resonant circuits, see B. Ulriksson, xe2x80x9cContinuous Varactor-Diode Phase Shifter With Optimum Frequency Response,xe2x80x9d IEEE Trans. On Microwave Theory and Tech., Vol. MTT-27, July 1979, pp. 650-654.
There is a need for analog phase shifters that are capable of operating at frequencies in the range of 1 to 18 GHz, wherein the phase shift can be electronically controlled.
Phase shifters constructed in accordance with this invention include a first rat-race ring having four ports, an input coupled to a first one of the ports, an output coupled to a second one of the ports, a first resonant circuit coupled to a third one of the ports, and a second resonant circuit coupled to a fourth one of the ports, each of the first and second resonant circuits including a tunable dielectric varactor.
A third resonant circuit can be connected in parallel with the first resonant circuit, and a fourth resonant circuit can be connected in parallel with the second resonant circuit. Each of the third and fourth resonant circuits can also include a tunable dielectric varactor.
In one embodiment, the first rat race ring can be connected to another phase shifting stage including a second rat race ring. Additional resonant circuits including tunable dielectric varactors can be connected to ports of the second rat race ring.
In another embodiment, the first rat race ring can be connected to a digital switched line phase shifting stage. The digital switched line phase shifting stage can include a first and second microstrip lines coupled to each other by first and second capacitors, an input coupled to the first microstrip line, and an output coupled to the second microstrip line, first and second PIN diodes connected between the first microstrip line and ground, third and fourth PIN diodes connected between the second microstrip line and ground, and means for applying a bias voltage to the first and second microstrip lines.